The present invention generally relates to optical fibers, and more specifically, to the interconnection of two optical conductors.
Fiber optic networks are being deployed at an ever-increasing rate due, at least in part, to the large bandwidth provided by fiber optic cables. Inherent with any fiber optic network design is the need to connect individual optical fibers to other optical fibers and to equipment. A common technique for connecting optical fibers is by terminating an optical fiber with a ferrule, and bringing the ferrule into a mating relationship with another ferrule terminating a second fiber. The ferrules are precisely aligned by a cylindrical sleeve which receives two ferrules of similar size and coaxially aligns the longitudinal axes of the respective cores thereof. The sleeve is typically a component of a coupler or adapter which securely couples together the plug housings of the respective optical fibers. Examples of such connection systems can be found in U.S. Pat. Nos. 4,738,507 and 4,738,508, both issued to Palmquist and assigned to the assignee of the present invention.
Recent advancements have led to the design of smaller optical fiber connection systems which utilize smaller diameter ferrules. The smaller ferrules offer the advantages of being more proportional in size to the fiber optic cable, offering improved axial alignment, and being more space efficient. In particular, the relatively smaller connectors can be more densely packed at the face of a piece of network equipment, and therefore, may provide more efficient space management.
The smaller connector design utilizes a ferrule that is 1.25 millimeters (mm) in diameter. An example of a smaller ferrule connector is the LC connector. Prior to the development of the smaller ferrule connectors, most connectors utilized ferrules that were 2.5 mm in diameter, which is twice the diameter of the ferrule of smaller ferrule connectors. An example of the larger ferrule connector includes the ST(trademark) (a trademark of Lucent Technologies Inc.) connector.
While there are numerous advantages of using the smaller ferrule connectors, some of which are set forth above, there is a compatibility problem with many of the existing optical networks that utilize the larger ferrule connectors. The larger ferrule connectors have been utilized for several years, and have been expansively deployed in optical networks. It is cost prohibitive in most situations to replace existing optical fiber networks with new optical fibers utilizing the smaller ferrule connectors. Therefore, when performing equipment or hardware upgrades or installations to existing optical networks, wherein the new equipment or hardware is designed for use with a smaller ferrule connection and the existing equipment or hardware is designed for use with the larger ferrule connectors, the technician is faced with the problem of how to interconnect two optical terminations having ferrules of dissimilar sizes. Thus, a need exists in the industry for an efficient and cost-effective method for interconnecting two different sized ferrules in an optimized mating relationship.
One proposed solution is the use of hybrid cables which have a larger ferrule connector on one end and a smaller ferrule connector on the opposite end. While such hybrid cables provide a relatively straightforward solution, they are relatively cumbersome to use, require two connections in order to interface two optic fibers (i.e., adding an additional connection), and are relatively expensive. Yet another proposed solution is a step sleeve adapter which comprises a cylindrical sleeve having coaxially aligned bores of different sizes formed into opposite ends of the sleeve and meeting in the middle thereof Accordingly, at approximately the middle of the step sleeve, the inside diameter of the sleeve, as defined by the bores, changes from a first inside diameter (corresponding to a smaller ferrule) to a second inside diameter (corresponding to a larger ferrule). This design requires precise sizing of the bores and the ferrules in order to establish and secure an accurate alignment of the ferrules within the sleeve. In practice, such precision is not consistently reproduced economically. Further, such step sleeves are typically made of a metal which has a high coefficient of thermal expansion thereby making the sleeve particularly sensitive to temperature changes. The step sleeve may be made of a ceramic material in the alternative, though a ceramic sleeve would be expensive to manufacture.
Therefore, an unsatisfied need exists in the industry for a low-cost connector for interconnecting optical conductors of dissimilar size with precision alignment of the respective cores thereof
The present invention provides for a V-groove adapter for interconnecting optical conductors of dissimilar sizes. For purposes of the present disclosure, an optical conductor can be, but is not limited to, a composite structure consisting of a connector ferrule into which an optical fiber has been set in and finished by, for example, polishing, or an optical fiber alone). Further, the references made herein to the dissimilar size of two optical conductors refers to the outside diameters of the respective optical conductors. A V-groove adapter in accordance with the present invention may comprise two axially aligned V-grooves of different predetermined dimensions (e.g., widths and depths) that are adapted to receive respective optical conductors, wherein the optical conductors are of different sizes. The V-grooves, which are part of an alignment member, support the two optical conductors in a predetermined aligned relationship, such as in axial alignment such that the respective cores of the optical conductors are coaxially aligned. Advantageously, the precise alignment of the two cores reduces the connection loss of the two optical fibers.
A V-groove adapter in accordance with the present invention can be mass produced using injection molding techniques, which are well-known and relatively low cost. The mold utilized in the injection molding is fabricated from a master V-block made of a monocrystalline material, such as silicon, that is prefabricated using masking and etching techniques commonly used in microelectronic device processing and fabrication. These techniques produce highly accurate features and can be precisely controlled to exacting dimensions. Thus, a V-groove adapter fabricated using an injection mold formed in accordance with the present invention can be inexpensively manufactured with a high degree of precision.
In accordance with an aspect of the present invention, an optical fiber adapter that aligns optical conductors comprises a first alignment member defining a first V-groove adapted to support therein a first optical conductor including a first central axis, and a second alignment member defining a second V-groove substantially axially aligned with the first V-groove and adapted to support therein a second optical conductor having a second central axis. The first V-groove and the second V-groove are configured to support the first and second optical conductors in a mating relationship which includes a predetermined alignment of the first and second central axes. The diameters of the first and second optical conductors may be different, and the first V-groove and the second V-groove may have different dimensions (e.g., width and depth) as necessary to provide the predetermined alignment. The predetermined alignment may include a coaxial alignment of the central axes, or an offset alignment of the central axes.
The width of a V-groove defines the height of the center of an optical conductor supported in the V-groove with reference to the top surface of the V-groove for an optical conductor of a given diameter. Accordingly, the width of the V-groove may be designed such that the V-groove coaxially aligns the central axis of the optical conductor with the central axis of the V-groove (which is at the top of the V-groove), or aligns the central axis of the optical conductor in an offset axial alignment with the central axis of the V-groove. If desired, a V-groove may comprise a trough or truncated cross section in order to preserve the structural portion of the connector beneath the V-groove, and to reduce the overall depth of the V-groove adapter.
In accordance with another aspect of the present invention, a method for making a mold for an optical fiber connector comprises the step of making a first V-groove of a first width and a second V-groove of a second width in a monocrystalline material, wherein the first V-groove and second V-groove are in a predetermined alignment with respect to one another. The resulting structure is referred to herein as a master V-block. A metal is deposited on the aligned first and second V-grooves, and then the monocrystalline material is removed to form a metal member having therein a negative impression of the aligned first and second V-grooves. The metal member is then used as a mold portion for making a V-groove adapter.
A method for making an optical fiber adapter comprises the steps of providing a mold defining a negative impression of a first V-groove and a second V-groove, wherein the first and second V-grooves are proximate one another and are disposed in a predetermined alignment with respect to one another. The mold is then used to form the optical fiber adapter having aligned third and fourth V-grooves, wherein each one of the third and fourth V-grooves is adapted to support therein an optical conductor so the respective optical conductors are in a predetermined axial alignment.
The predetermined alignment of the optical conductors may be coaxial alignment or offset alignment, as may be desired. Accordingly, the V-groove adapter may be utilized to interconnect two optical conductors which having different outside diameters. The V-groove adapter may be fabricated utilizing injection molding techniques so that the V-groove adapter can be mass produced. The V-groove adapter preferably comprises plastic material. In order to account for the shrinkage in the plastic during the injection molding process, the first and second V-grooves of the mold may be made slightly larger than the third and fourth V-grooves of the resulting adapter.
In accordance with another aspect of the present invention, an optical attenuator comprises a first alignment member defining a first V-groove of a first width, wherein the first V-groove is adapted to support therein a first optical conductor, and a second alignment member defining a second V-groove of a second width, wherein the second V-groove is adapted to support a second optical conductor. The first and second V-grooves are configured to support the first and second optical conductors in an axial alignment with respect to one another that is slightly offset. The axial offset may be lateral or vertical or both, and is precisely controlled to provide a predetermined loss in the optical signal passing from the emitting optical conductor to the receiving optical conductor. By precisely controlling the widths of the first and second V-grooves, optical conductors of the same or different diameters may be interconnected by an optical attenuator in accordance with the present invention.
In accordance with yet another aspect of the present invention, an optical fiber adapter for establishing an offset launching condition of an optical signal from a single-mode fiber to a multimode fiber comprises a first alignment member defining a first V-groove of a first width, wherein the first V-groove is adapted to support therein an optical conductor having a multimode core, and a second V-groove of a second width, wherein the second alignment member defining a second V-groove is adapted to support therein a second optical conductor having a single-mode core. The first V-groove and the second V-groove are axially offset by a predetermined amount with respect to one another so that the optical signal injected from the single-mode core into the multimode core underfills the optical modes of the multimode core. The axial offset may be lateral, vertical or in between.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention as defined by the appended claims.